Amorphe Silizium-Kohlenstoff-Filme für Dünnschichtsolarzellen auf der Basis von Silylmethanen

Fölsch, J.

Book/Report

FZJ-2019-01046

Amorphe Silizium-Kohlenstoff-Filme für Dünnschichtsolarzellen auf der Basis von Silylmethanen

Fölsch, J. (Corresponding author)FZJ*

1995
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Jülich : Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Berichte des Forschungszentrums Jülich 3147, 114 p. (1995)

Please use a persistent id in citations: http://hdl.handle.net/2128/21509

Report No.: Juel-3147

Abstract: Hydrogenated amorphous silicon-carbon alloys (a-SiC:H) are of considerable interest for optoelectronic devices, especially for thin film solar cells. With the conventionally used mixture of silane (SiH$_{4}$) and methane (CH$_{4}$) for the plasma deposition (PE-CVD) of a-SiC:H the optoelectronic properties deteriorate strongly with increasing carbon content. In this work, alternative carbon containing gases (namely di-, tri-and tetrasilylmethane) were used. The main idea of using these gases is that the molecules already contain network-building Si-C bonds, so that material with a good Si-C network structure was to be expected. For the optimized material of this work, the optoelectronic properties of methane based and silylmethane based films are very good, and also very similar. All films show low hydrogen contents, low Urbach energies and low defect densities. The investigation of the binding structure of these materials shows thattwo different kinds of solid a-SiC:H films exist: in one class, the methane based alloys, hydrogen and carbon are mainly incorporated through CH$_{3}$ groups, forming microvoids in the network. In the other class, the silylmethane based layers, carbon is mainly bound in two configurations, i.e. in a silicon environment with tetrahedral coordination, and through CH groups incorporated in the Si-C network. In the latter class, the hydrogen is mainly bound to silicon, giving rise to the formation of voids as a consequence of (SiH$_{2}$)n and (SiH$_{3}$) groups. Therefore, the improvement in the optoelectronic properties of silylmethane based a-SiC:H, expected due to the lower concentration of CH$_{3}$ groups and higher concentration of Si-C bonds in comparison to methane based material, is compensated by the higher portion of hydrogen bound to silicon atoms. The comparison of the infra red absorption spectra of both classes of a-SiC:H material leads to the conclusion, that the energetic position of the Si-C stretching vibration depends on the local environment and on the composition of the material. In methane based films, the mode is located at a wavenumber of 770 cm$^{-1}$ for Si-CH$_{3}$ groups (here, the Si-C oscillators are vibrating on inner surfaces). For silylmethane based films, the Si-C stretching mode is broadened and shifted towards lower energies at 740 to 760 cm$^{-1}$ wavenumbers, due to the fact, that carbon is mainly incorporated as an atom or as a CH group in a silicon network. In a dense environment, the Si-C oscillator is vibrating at 730 cm$^{-1}$ wavenumbers.

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